[Bug]: Warning: Undefined array key "enabledThemes" + TypeError: join(): Argument #1 ($pieces) must be of type array, string given

### ⚠️ This issue respects the following points: ⚠️

- [x] This is a **bug**, not a question or a configuration/webserver/proxy issue.
- [x] This issue is **not** already reported on [Github](https://github.com/nextcloud/server/issues?q=is%3Aopen+is%3Aissue+label%3Abug) OR [Nextcloud Community Forum](https://help.nextcloud.com/) _(I've searched it)_.
- [x] Nextcloud Server **is** up to date. See [Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) for supported versions.
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/).

### Bug description

```
ErrorException: Warning: Undefined array key "enabledThemes"
ErrorException: Warning: Undefined array key "enabledThemes"
#10 /var/www/nextcloud/core/templates/layout.guest.php(40): include
#9 /var/www/nextcloud/lib/private/Template/Base.php(161): OC\Template\Base::load
#8 /var/www/nextcloud/lib/private/Template/Base.php(131): OC\Template\Base::fetchPage
#7 /var/www/nextcloud/lib/private/legacy/OC_Template.php(117): OC_Template::fetchPage
#6 /var/www/nextcloud/lib/private/legacy/OC_Template.php(148): OC_Template::fetchPage
#5 /var/www/nextcloud/lib/public/AppFramework/Http/TemplateResponse.php(189): OCP\AppFramework\Http\TemplateResponse::render
#4 /var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php(159): OC\AppFramework\Http\Dispatcher::dispatch
#3 /var/www/nextcloud/lib/private/AppFramework/App.php(161): OC\AppFramework\App::main
#2 /var/www/nextcloud/lib/private/Route/Router.php(307): OC\Route\Router::match
#1 /var/www/nextcloud/lib/base.php(1073): OC::handleRequest
#0 /var/www/nextcloud/index.php(24): null
```

```
TypeError: join(): Argument #1 ($pieces) must be of type array, string given
#11 /var/www/nextcloud/core/templates/layout.guest.php(40): join
#10 /var/www/nextcloud/core/templates/layout.guest.php(40): include
#9 /var/www/nextcloud/lib/private/Template/Base.php(161): OC\Template\Base::load
#8 /var/www/nextcloud/lib/private/Template/Base.php(131): OC\Template\Base::fetchPage
#7 /var/www/nextcloud/lib/private/legacy/OC_Template.php(117): OC_Template::fetchPage
#6 /var/www/nextcloud/lib/private/legacy/OC_Template.php(148): OC_Template::fetchPage
#5 /var/www/nextcloud/lib/public/AppFramework/Http/TemplateResponse.php(189): OCP\AppFramework\Http\TemplateResponse::render
#4 /var/www/nextcloud/lib/private/AppFramework/Http/Dispatcher.php(159): OC\AppFramework\Http\Dispatcher::dispatch
#3 /var/www/nextcloud/lib/private/AppFramework/App.php(161): OC\AppFramework\App::main
#2 /var/www/nextcloud/lib/private/Route/Router.php(307): OC\Route\Router::match
#1 /var/www/nextcloud/lib/base.php(1073): OC::handleRequest
#0 /var/www/nextcloud/index.php(24): null
```

happening at

```php
		<?php emit_script_loading_tags($_); ?>
		<?php print_unescaped($_['headers']); ?>
	</head>
	<body id="<?php p($_['bodyid']);?>" <?php foreach ($_['enabledThemes'] as $themeId) {
		p("data-theme-$themeId ");
	}?> data-themes="<?php p(join(',', $_['enabledThemes'])) ?>">
		<?php include 'layout.noscript.warning.php'; ?>
		<?php include 'layout.initial-state.php'; ?>
		<div class="wrapper">
			<div class="v-align">
				<?php if ($_['bodyid'] === 'body-login'): ?>
```

### Steps to reproduce

1. ???


### Expected behavior

No error

### Nextcloud Server version

31

### Operating system

None

### PHP engine version

None

### Web server

None

### Database engine version

None

### Is this bug present after an update or on a fresh install?

None

### Are you using the Nextcloud Server Encryption module?

None

### What user-backends are you using?

- [ ] Default user-backend _(database)_
- [ ] LDAP/ Active Directory
- [ ] SSO - SAML
- [ ] Other

### Configuration report

```json

```

### List of activated Apps

```shell

```

### Nextcloud Signing status

```shell

```

### Nextcloud Logs

```json

```

### Additional info

_No response_

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Uh oh!

[Bug]: Warning: Undefined array key "enabledThemes" + TypeError: join(): Argument #1 ($pieces) must be of type array, string given #51948

⚠️ This issue respects the following points: ⚠️

Bug description

Steps to reproduce

Expected behavior

Nextcloud Server version

Operating system

PHP engine version

Web server

Database engine version

Is this bug present after an update or on a fresh install?

Are you using the Nextcloud Server Encryption module?

What user-backends are you using?

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

Metadata

Assignees

Labels

Type

Fields

Projects

Milestone

Relationships

Development

Uh oh!

[Bug]: Warning: Undefined array key "enabledThemes" + TypeError: join(): Argument #1 ($pieces) must be of type array, string given #51948

Description

⚠️ This issue respects the following points: ⚠️

Bug description

Steps to reproduce

Expected behavior

Nextcloud Server version

Operating system

PHP engine version

Web server

Database engine version

Is this bug present after an update or on a fresh install?

Are you using the Nextcloud Server Encryption module?

What user-backends are you using?

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

Metadata

Metadata

Assignees

Labels

Type

Fields

Projects

Milestone

Relationships

Development

Issue actions